This invention relates generally to imaging systems and more particularly to an imaging system that produces multiple images of a single object scene onto a single detector array. These multiple images are spatially displaced from one another on a single detector array in the image plane.
In some specialized applications, such as long-range multi-spectral imaging, there is a great desire to produce several images of a given object scene simultaneously on a single detector array (such as a CCD). For applications such as multi-spectral imaging, each of these separate images is passed through a different colored filter. Presently, multi-spectral imaging is typically performed either with rotating filter wheels (which are unable to record more than a single image simultaneously) or with a plurality of imaging and detection systems (which inherently are unable to image onto a single detector array).
Multi-spectral systems that rely on rotating filter wheels produce images through various filters, one-at-a-time, and in succession. In cases where it is important to produce differently-filtered images simultaneously, filter-wheel-dependent multi-spectral systems are inadequate.
U.S. Pat. No. 5,194,959 describes a multi-spectral imaging system that produces differently-filtered images simultaneously on three different imaging sensors. One major drawback with this system is that three imaging sensors, which can often be quite expensive, are required. In addition, in cases where high-performance and/or low-contrast imaging is to be performed, it is desirable to compare images formed on a single imaging sensor. The reason for this is that every imaging sensor, no matter how similar, is different in some way than every other imaging sensor, especially through a large range of illumination levels. For example, something as simple as a slight difference in temperature stability between two imaging sensors can make very fine comparisons of images made on the two imaging sensors practically impossible. For many multi-spectral applications, it is absolutely necessary to produce multiple images on a single imaging sensor.
U.S. Pat. Nos. 4,933,751, 5,024,530, 5,642,191, 5,729,011, and 5,926,283 each describe an apparatus and/or method for producing multiple images simultaneously on a single imaging sensor. All of these prior art patents have shortcomings, which are directly addressed in the invention described herein.
U.S. Pat. Nos. 4,933,751 and 5,926,283 describe apparatuses that require mirror reflection of the optical beam in “off-axis” or “perpendicular” directions. Because of the convoluted orientation of the multiple off-axis mirrors in these designs, complex positioning systems are required.
U.S. Pat. No. 5,729,011 describes an apparatus that positions the image-separating prism at a point in the optical train where the light is converging. Whereas positioning of the prism at a point in the optical train where light is collimated would produce sharp, well-resolved images, positioning of the prism at a point in the optical train where light is converging introduces a number of aberrations and degrades image quality. Therefore an apparatus that positions the prism at a point in the optical train where light is converging is inferior to one that takes care to position the prism in a collimated-light space.
U.S. Pat. Nos. 5,642,191 and 5,024,530 describe apparatuses in which splitting of the image into only two images is anticipated, and means are not shown for the more complex case where four or more images are to be produced. Furthermore, these patents require several imaging lens systems in order to create a first image, collimate the light, and then to form a second image. These multiple imaging lens systems more costly, larger, and cause more imaging aberrations than the single imaging lens system described in the present invention.
It is therefore an object of this invention to produce multiple images of the same object scene simultaneously and adjoining one another on a single detector plane.
It is another object of this invention to effect such imaging with an optical system that exhibits no vignetting (obscuration of a portion of the light reaching the detector).
It is another object of this invention to effect such imaging with an optical system that requires no off-axis optical elements.
It is another object of this invention to effect such imaging with a single optical imaging lens system.
It is another object of this invention to effect such imaging without the need for mirrors.